A vehicle waste heat recovery device including a Rankine cycle as disclosed in Japanese Unexamined Patent Application Publication No. 2005-42618 has been known as a typical technique. The vehicle waste heat device including the Rankine cycle is configured to exchange heat between combustion gas discharged from an engine and working fluid circulating in the Rankine cycle in a steam generator, thereby recovering engine waste heat. An expander is configured to expand the high-temperature high-pressure working fluid heated by the steam generator to generate an output. A heat exchanger is configured to exchange heat between the working fluid having expanded by the expander and engine coolant water circulating in an engine coolant water circuit, thereby condensing the working fluid.
However, the vehicle waste heat utilization device disclosed in Japanese Unexamined Patent Application Publication No. 2005-42618 uses engine coolant water having been used for engine cooling to condense the working fluid. Thus, the working fluid cannot be sufficiently condensed in the heat exchanger. For this reason, there is a problem that the Rankine cycle cannot be sufficiently operated due to a high condensation pressure.
On the other hand, in a vehicle waste heat recovery device including a Rankine cycle as illustrated in FIG. 2 of Japanese Unexamined Patent Application Publication No. 2013-160076, coolant water on an upstream side of a radiator is used as a heat source of a steam generator for the purpose of solving the above-described problem. A condenser as a heat exchanger is configured to exchange heat between working fluid and coolant water on a downstream side of the radiator configured to cool coolant water of an internal combustion engine. As described above, in the condenser of Japanese Unexamined Patent Application Publication No. 2013-160076, heat is exchanged between low-temperature coolant water cooled by the radiator and the working fluid. This decreases a condensation pressure, leading to a high thermal efficiency of a heat engine. Thus, Japanese Unexamined Patent Application Publication No. 2013-160076 discloses the effect of providing a great amount of waste heat regeneration.